I mentioned below that the strictures around alcohol levels in the bourbon distilling and aging processes may come off as a little esoteric to the non-specialist. I suppose they will, however you are about to become a specialist in whiskey distillation, so that shouldn’t frighten you. Read on!
All distilled spirits start out as beer, basically. A “mash” is made out of grain and water, that mash is then allowed to ferment. The trouble is, most brews like that (think beer, wine and hard cider) rarely exceed an alcohol content of 12 % or so. To get something with a little more kick to it, you have to “distill” the alcohol out of it. This is achieved by heating it, which causes the alcohol to evaporate, condense in tubes, and drip into a collecting vessel (I’m greatly over-simplifying, but you get the idea).
This process doesn’t yield pure alcohol, and that’s a good thing from the standpoint of flavor. If whiskey were pure alcohol, it wouldn’t taste like anything (plus it would kill most of us). It’s those “other things” that travel with the alcohol molecules as they evaporate that give the whiskey character. This is why, by law, bourbon cannot be distilled to a higher alcohol content than 80% (160 proof).
However it’s what goes on in the barrel after distillation that I find to be the most interesting. Whiskey is usually diluted with water to some degree when it’s barreled. The reason for this again has to do with flavor. Oak wood contains a wide range of chemical compounds that can potentially add flavor to a whiskey, however they need to be dissolved so they can disperse. Some of them are alcohol-soluble, but others can only be dissolved with water. And as it turns out, many of the water-soluble flavors are the most desirable: the vanilla- and caramel-like notes. The more water the barrel contains, the more of these flavors leech out. (For more extended blah-blah-blah on flavor solvents, see this post from two years ago).
The problem is that taking up valuable barrel space with water is not something that accountants working for large distillers like very much. From a pure cost perspective, cramming as much alcohol as you can into a given barrel, letting it soak up as much alcohol-soluble flavor as it can get, then diluting it with water after it has aged (in the minimum amount of time, of course) makes the most sense. Though again, that process ultimately robs the consumer of the best possible bourbon experience.
What’s interesting is that from the bourbon distiller’s perspective, five or six years in the barrel is the most you’d want to age a whiskey. Much after that — or so it’s thought here in Kentucky — most of the flavor the barrel has to offer has been removed. What do you do with the barrel after that? Odds are, you sell it to the Scots, who habitually age their whiskey for periods of 20 years or more. Does that make Scotch whiskey better? It depends on your point of view. From the standpoint of a Kentuckian, the Scots have to age their whiskey that long because it takes twenty years to get what flavor is left in the wood out of it.
Kentuckians would rather make their whiskey (relatively) fast and drink it (relatively) young. This attitude, for some whiskey purists, is proof that Kentucky bourbon will be forever inferior to its Old World predecessors, cheap hooch compared to the real thing. Maybe it’s because I’m a Kentuckian now, but I’ve come to see the flaw in this line of reasoning, and come to understand the limits of what age can contribute to a barrel of booze.